RIVER Noise and vibrations report

Transcription

1 RIVER Noise and vibrations report Date of Issue : September 3, 2009 Paul-Edouard GOLLE MASSON MARINE 5 rue Henri Cavallier Saint Denis les Sens FRANCE pe.golle@masson-marine.com Company Restricted The information contained in this document is MASSON MARINE property. Disclosure to third parties or reproduction in any from whatsoever without written consent is forbidden.

2 Contents 1 General specifications 3 2 Sound measurements Microphone positions Overall noise for different speed Waterfalls Full forward Noise when manoeuvring Propeller noise? Vibrations measurements Full forward Waterfall sensor input shaft axial Ceiling isolation Conclusion 13 2

3 MASSON MARINE RIVER Measurements report September 3, General specifications SHIP IDENTIFICATION Name RIVER Reg N Test date 20 août 2009 Type Tanker Length 125 m Country NL PROPELLER Type FPP / NOZZLED Brand AMV Blade N 5 Line shaft L Diameter 1800 mm ENGINE Brand/Type CATERPILLAR / V16 Model 3516 SN TTD00261 Power rpm Rotation CCW Mounting Flexible Flexible GEARBOX Type MMW16500 SN Ratio 4.95 Rotation CW Mounting Rigid Oil SAE 30 PTO Type 0 PTI No Trailing P No Observations Engine room door opened during measurements, tanks fully loaded, ventilation is switched on (except if the contrary is mentioned). Ship is finished, the crew is complaining about a noise appearing at low speed and the two aft cabins do have a noise level above regulations. No measurements have been done in living quarters. The table below give the gear excitation of each gear mesh according to the engine speed N express in revolutions per minute and the order n (n = 1 main gear mesh frequency, n = 2 harmonic 2 of gear mesh,... ). K i K 2 K pto K pump h n (N) = 50n N 60 h n (N) = 20n N 60 h n (N) = 79.45n N 60 h n (N) = 19.86n N 60 Tab. 1: Gear mesh excitations according to engine speed and harmonic number

4 4 MASSON MARINE RIVER Measurements report September 3, Sound measurements 2.1 Microphone positions Two microphones were used during the sea trail, one was placed close to the gearbox k 2 inspection cover (1), about 20 cm in order to really mesure what is coming from the gearbox. The second one was placed about 50 cm above the engine (2). Note For shipping inspection the distance should be 100 cm Fig. 1: Microphone on the gearbox, 20 cm from inspection cover Fig. 2: Microphone beyond the engine, 50 cm from engine 2.2 Overall noise for different speed Fig. 3: Overall SPL (dba), sailing forward As you can notice the noise in the engine room is not high. The Sound Pressure Level (SPL) when sailing forward is rpm on microphone at 20 cm from gearbox. 2.3 Waterfalls The waterfall view is a 3 dimensional diagram representation. In our case frequency correspond to the X-axis, engine speed correspond to Y-axis and the Z-axis (here the colors, defined by the scale on the left) represent the value corresponding to this speed and frequency.

5 MASSON MARINE RIVER Measurements report September 3, Fig. 4: SPL profile during an engine run up (650 up to 1550 rpm), gearbox microphone On this waterfall we can identify one gear order which seems to be harmonic 5 of K2 and is discussed later in this report. Also the engine turbo clearly appear as a strong noise generator. The same graph is displayed below, viewed from the engine microphone. Fig. 5: SPL profile during an engine run up (650 up to 1550 rpm), engine microphone The gear order can still be perceive but start to disappear in the surrounding noise. The gear noise is the same but as the distance between gearbox and microphone is higher the level corresponding to the gear order and catch by the microphone is lower. On the other hand as we get closer to the turbo with the second microphone, its excitation c MASSON MARINE 2009

6 6 MASSON MARINE RIVER Measurements report September 3, 2009 seems stronger... Also always watch out carefully the color scale for each display, because the maximum value recorded is always showed with a dark red whether it is 50 dba or 100 dba. In our case maximum value is 108 dba for the gearbox microphone whereas it is dba for the engine microphone. 2.4 Full forward The overall SPL was dba average on 30 s under 1600 rpm at the gearbox microphone. On the graph 6 I listed some gears orders that can be identify. Orders 1, 2, 4, 5 of K 2 gear mesh are present (designed by marker 1-x, where x stands for the order), as well as order 1 of pump gears and orders 2, 3, 4 and 5 from the K P T O gears. Please refer to the graph for the value of each. Fig. 6: SPL profile in dba average on 30s at 1600 rpm, sailing forward I also use the max peak marker in order to determine the 5 first maximum level, the results are listed in the table below. Peak n f [Hz] Level [dba] Tab. 2: Main peaks and their matches when sailing forward at 1600 rpm Only order 1 of K 2 gear mesh appear in the 5 maximum level given by the peak marker function. You also notice the turbo noise which creates quite a wide band frequency excitation. The power band marker (see graph 7)allowed me to quantify the total power

7 MASSON MARINE RIVER Measurements report September 3, contained in its excitation band from 10.4 khz up to 11.4 khz roughly. The turbo noise is equivalent to a 88.7 dba noise generator, although its maximum peak is 82 dba. Fig. 7: SPL profile in dba average on 30s at 1600 rpm, sailing forward 2.5 Noise when manoeuvring The owner also hear a noise when he is manoeuvring with steering, unfortunately I could not notice a strong noise variation implying the consequence of steering. The graph 8 shows the noise measured during 30 s while the captain was steering. The reason can simply be that the microphone is not at the best place to record this noise variation. Fig. 8: Waterfall view of noise on 30 s period, steering and sailing forward 1500 rpm

8 8 MASSON MARINE RIVER Measurements report September 3, Propeller noise? During the sea trail we also notice that there is a noise when running at idling speed until 1000 rpm roughly. The level measured by the sensors on the gearbox does not show variations denoting something wrong inside the gearbox. I must say that the sensors were placed to diagnose an eventual problem on the gearbox not on the propeller... However when we really zoom into the engine or gearbox microphone we can see a lot of sidebands spaced of 8 Hz (for 965 rpm engine speed). Fig. 9: Zoomed average spectrum of engine mic, 15 average, 0.5 Hz resolution, forward 965 rpm To have a better view of this sidebands the cepstrum is displayed below. The cepstrum is the Fast Fourrier Transformation of the spectrum. The x-axis represent the Quefrency in s. Fig. 10: Cepstrum view of spectrum 9

9 MASSON MARINE RIVER Measurements report September 3, You may think that the peaks appearing on the cepstrum are harmonics but the space between them is not constant (1.5, 2). Also they are not in entire order of the output shaft speed (0.825, 1.23, 2.47). I even compared with the output shaft bearings defect frequencies, nothing match. 3 Vibrations measurements Vibrations at several points have been collected, not all of them are displayed here cause they do not present a particular interest. Fig. 11: Some sensor placements on the gearbox 3.1 Full forward Fig. 12: Vibration profile at input shaft axial sensor

10 10 MASSON MARINE RIVER Measurements report September 3, 2009 If you look to the graph 12, you will noticed that the vibration level is very low, the overall valus is g and order 1 of K 2 is only 0.2 g. According to the standard AFNOR E the level on the gearbox is very low. The standard classified machines thanks to their overall speed value on the 10 Hz Hz bandwidth. A good machine in term of vibration has its value under 2.8 mm/s, the value here is 2.68 mm/s (graph 13). Fig. 13: Velocity obtained from graph 12, 2.68 mm/s overall 3.2 Waterfall sensor input shaft axial Fig. 14: Waterfall representation of acceleration at input shaft axial sensor On fig.14, you can see some diagonal lines that correspond to the K 2 gear mesh harmonics. In order to better compare their level, I extract the 6 first orders (graph 15).

11 MASSON MARINE RIVER Measurements report September 3, Fig. 15: 6 first orders of K 2 which are orders 20, 40,... of input shaft speed (see table 1 The extraction graph shows that order 1, 2 and 5 have the highest contribution on the vibration measured at this point. Also we can notice that each order level is influenced by speed and the vibration produce does not necessary increase with rotation speed. 3.3 Ceiling isolation In the second half of measurement I placed one sensor on the ceiling in order to check its isolation against vibration. The two following graphs shows the difference between one sensor on the gearbox and one sensor on the ceiling. Fig. 16: Engine room ceiling isolation, sailing forward 1600 rpm

12 12 MASSON MARINE RIVER Measurements report September 3, 2009 Fig. 17: Engine room ceiling isolation, sailing backward 1600 rpm 4 Conclusion According to the measurements the gearbox does not create high noise level, and it is always below the regulations. The vibrations created by the gear meshes are very low, which means that the vibrations transmit by the gearbox to the ship structure is also low. According to AFNOR standard due to its low overall velocity level, this gearbox is classified in the good range. Moreover the vibration isolation of the ceiling seems all right, and the noise that the owner is complaining about is not linked to the gearbox so I advice looking more on the propeller side.